Why frost fighting is so important to our vines
When many people think of New Zealand, they think of warm sunny summers and relatively mild winters, however this is definitely not the case down in the South Island and in the case of McArthur Ridge and Shaky Bridge, two of the world’s southernmost vineyards, this means extremely changeable weather conditions which need to be constantly monitored in order to keep the vines healthy and ready to produce the award-winning wine each year.
The McArthur Rudge vineyard has its own weather station for monitoring temperatures with 14 temperature sensors spread throughout the vineyard. Each of the sensors has an alarm which activates the phone of vineyard manager Murray Petrie when critical temperatures are reached. From then, it’s all hands to the pump, deciding on the best course of action and determining the type of frost that could be affecting the vines.
You may not know this but there are a number of different types of frost and we have to deal with each one in a slightly different way.
Advective frost – also known as ‘wind frost’ refers to tiny ice spikes that occur when there is a very cold wind blowing and can occur day or night.
Radiation frost – also known as ‘hoar frost’ refers to white ice crystals deposited on the ground or loosely attached to exposed objects including leaves. It occurs when clear, cold, dry air masses move into the area and causes the plant tissue to become colder and colder.
Dew point – dew point is the temperature at which dew forms on the leaves. As the air cools, vapour in the air begins to form, and this temperature can be above or below freezing point.
Tackling frost on the vines
Once we have decided that our frost protection system needs to be started, the water we are applying to the vines starts freezing on the plant. As the ice is forming around the plant it releases energy (latent heat) and this heat keeps a small thin layer of water around the plant above zero degrees, protecting the plant from the frost.
McArthur Ridge has two pumping stations and two dams where the water is pumped both for frost fighting and irrigation. One dam holds 115,000 cubic metres and the other 220,000 cubic metres (an olympic-size swimming pool has 2,500 cubic metres of water). The bottom 60ha of the development can be protected for up to 6 consecutive eight hour frost fighting events in a row, the top 120ha can be protected for up to 4 consecutive eight hour frost fighting events in a row.
Other vineyards in New Zealand also use helicopters to tackle the frost by pushing warmer air down onto the vines but the temperatures are often too cold down in the Central Otago for this to be effective.
Protecting the early buds is so crucial to ensuring a healthy vintage so the spring time is one of the most nervous times for all wine enthusiasts but our wine making experts who make up the New Zealand Wine Co-Op have years of experience in dealing with frost, especially being based so far south so they know exactly what they are doing and when they need to do it.
Hopefully this has given you an insight into how vineyards in the Central Otago cope with spring frosts and helps you to understand the love and care that goes into every bottle of Central Otago Pinot Noir.